The present invention relates to a new and distinctive cantaloupe inbred line, designated I446, a hybrid cantaloupe designated I446*I444, and a hybrid cantaloupe designated I446*I407. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, field performance, fruit and agronomic quality such as sugar levels, small cavity size, flesh color or texture, rind firmness or strong net, resistance to diseases and insects, and tolerance to drought and heat.
Practically speaking, all cultivated forms of cantaloupe belong to the highly polymorphic species Cucumis melo L. that is grown for its sweet edible fruit. The term cantaloupe, as used herein, refers to the American usage of the term which is used to describe the netted melons commonly referred to as cantaloupe or muskmelon in U.S. commerce. As a crop, cantaloupes are grown commercially wherever environmental conditions permit the production of an economically viable yield. They are produced on non-climbing vines that are cultivated prostrate on the soil. On healthy plants there is a canopy of large, soft, hairy leaves, generally heart shaped and somewhat lobed. Fruits may be orange fleshed or green fleshed. The fruit surface is generally netted and roughened and in some varieties sutured. Fruit shape is generally round to oval and ranges in size from five to eight inches long and about equal in diameter. In the United States, the principal fresh market cantaloupe growing regions are California, Arizona and Texas which produce approximately 96,000 acres out of a total annual acreage of more than 113,000 acres (USDA, 1998). Fresh cantaloupes are available in the United States year-round although the greatest supply is from June through October. Fresh cantaloupes are consumed in many forms. They are eaten sliced or diced and used as an ingredient in many prepared foods.
Cucumis melo is a member of the family Cucurbitaceae. The Cucurbitaceae is a family of about 90 genera and 700 to 760 species, mostly of the tropics. The family includes pumpkins, squashes, gourds, watermelon, loofah and several weeds. The genus Cucumis, to which the cantaloupe, cucumbers, and several melons belong, includes about 70 species. Cucumis melo includes a wide range of cultivated plants. Although crosses outside the species are sterile, intraspecific crosses are generally fertile, resulting in a confusing range of variation. The more common cultivated plants fall into four main groups. First are the true cantaloupes of Europe. These have thick, scaly, rough, often deeply grooved, but not netted rinds. Second are the muskmelons, mostly grown in the United States, where they are incorrectly called cantaloupes. These have finely netted rinds with shallow ribs. Third are the casaba or winter melons with large fruits. These have smooth, often yellow rinds. The honeydew melons are in this third group. Fourth are a group of elongated melons of India, China and Japan which are grown as vegetables. Other classification schemes and cultivars could be presented.
Cantaloupe is a simple diploid species with twelve pairs of highly differentiated chromosomes. Large field spaces are required for cantaloupe and the need for labor intensive hand pollination for self as well as cross pollination has resulted in a lag in the knowledge of cantaloupe genetics relative to such crops as tomato. Cantaloupe flowers open after sunrise; the exact time depends on environmental conditions such as sunlight, temperature and humidity. The flower closes permanently in the afternoon of the same day. Almost all pollen is collected and transferred before noon. Typically flowers are staminate although some are also hermaphroditic. Although hermaphroditic flowers are self-fertile, they are incapable of performing self-pollination. Insects are required for pollination. The primary pollinators are bees, particularly honey bees.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, recurrent selection, and backcross breeding.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars, nevertheless, it is also suitable for the adjustment and selection of morphological characters, color characteristics and simply inherited quantitative characters. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested per se and in hybrid combination and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for use as parents in new commercial cultivars; those still deficient in a few traits may be used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to twelve years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a focus on clear objectives.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of cantaloupe breeding is to develop new, unique and superior cantaloupe inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated self pollination or selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. This unpredictability results in the expenditure of large research monies to develop a superior new cantaloupe inbred line.
The development of commercial cantaloupe hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents possessing favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1s or by intercrossing two F1s (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable cultivars or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. After the initial cross, individuals possessing the phenotype of the recurrent parent and the trait of the donor parent are selected and repeatedly, crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Principles of Plant Breeding″ John Wiley and Son, pp. 115-161, 1960; Allard, 1960; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny.
Cantaloupe is an important and valuable vegetable crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding cantaloupe hybrids that are agronomically and commercially sound. The reasons for this goal are to maximize the amount of fruits produced on the land used (yield) as well as to improve the fruit agronomic qualities. To accomplish this goal, the cantaloupe breeder must select and develop cantaloupe plants that have the traits that result in superior parental lines that combine to produce superior commercial hybrids.